Electrophysiological correlates of visual impairments after traumatic brain injury

Our aims were to investigate: (i) the VEP correlates of functional visual impairments following traumatic brain injury (TBI), in particular of the reduced spatial form perception; and (ii) the VEP correlates of visual sustained arousal in TBI patients. We used two approaches: (i) the analysis of latency and amplitude of the peaks; and (ii) the study of the correlations among the latencies of the peaks as a label of temporal synchronization. Thirty-five severe TBI outcome inpatients and 35 matching controls were studied. Pattern-reversal VEPs were recorded at Oz-Fz and Cz-A1, first without counting, then with counting of the reversals. Seven peaks of the waveform at Oz and eight peaks at Cz were measured. We found several differences in amplitude and latency between patients and controls, and between nocount/count. The temporal binding of the peaks within each channel and between the two channels was calculated by correlation matrices, and tested by factor analysis. Results indicated that the synchronization of the peaks within each channel did not differ between patients and controls. The temporal covariation between peaks occurring at Oz and Cz, however, was highly significantly altered in patients. This suggests that visual impairments in TBI patients may be due to a deranged synchronization of the activity of different brain regions.